Spark plug



Dec. 23, 1941. T. G. MCDOUGAL SPARK PLUG Filed July 27, 1940 3maentorPatented Dec. 23, 1941 SPARK PLUG Taine G. McDougal, Flint, Mich.,assignor to General Motors Corporation, Detroit, Mich, a corporation ofDelaware Application July 27, 1940, Serial No. 348,056

9 Claims.

This invention has to do with spark plug electrodes and method ofassembling and sealing same in the usual bore in the insulator. It is animprovement on the invention described and claimed in Patent No.2,106,578 igranted to Schwartzwalder and Kirk on January 25, 1938. Inthat patent there is disclosed an electrode consisting of two axiallyseparated parts secured to each other and to the insulator by anintermediate conducting glass seal. The lower electrode part cooperateswith the usual side electrode to provide a spark gap while the upperelectrode part constitutes the terminal to which the spark plug lead issecured. In the assembly in the upper end of the bore. Thereafter theassembly is heated to partially fuse or soften the glass whereupon theupper part of the electrode is forced down into the glass causing it tobe squeezed into the space between the electrode and the insulator bore.The glass adheres fairly well to the electrode parts and tenaciously tothe insulator and, upon hardening, forms a strong, tight seal and at thesame time, owing to its conducting property, allows passage of currentto the sparking end of the electrode.

An important feature of my invention consists in the provision of meansto limit the extent of movement of theupper part of the electrode intothe insulator bore during assembly. This not only insures uniformity inthe product but in sures the presence of conducting glass between theends of the electrode sections rather than metal to metal contact. Thisglass, while soft, accommodates itself to any variations in length ofthe sections of the electrode.

It is also frequently desirable to employ an electrode having anenlarged end at the spark gap. The head is preferably of such shape asto form a tight seal with the end of the insulator preventing hotcombustion gases from entering the insulator bore and attacking theelectrode metal. With such constructions it is necessary to provide somemeans for gripping the upper end or the electrode section to hold it inplace. Because the bonding of the glass seal to the upper end of thelower electrode section may not remain stable in service for thispurpose I have preferred to provide as an additional safeguard some formof mechanical interlock. Thus the upper end of the lower section may beexpanded sition. Such insulators areornvetedovertolocktheelectrodelectionin place or it may be so shaped orroughened as to mechanically interlock with the glass seal. It may bedesirable to provide a washer 0r gasket, preferably of soft metal,around the lower electrode section and resting on thebottom ofthe upperpart of the electrode bore to prevent the glass seal when softenedduring assembly from penetrating into the lower part of the electrodebore.

In application Serial No. 343,808 filed on July 3, 1940, bySchwartzwalder and Rulka it is proposed to employ two glass pelletsinstead of one for forming the seal. One pellet is of such compositionthat it softens but slightly during assembly. This pellet is placed inthe lower part of the insulator bore, secures the electrode in place andforms a good seal with the insulator. The upper pellet is less heatresistant and becomes more fluid upon heating during assembly, and flowsabout the upper section of the electrode and forms a good bond with theelectrode metal, the insulator and the remainder of the glass. Anotherfeature of my invention consists in the use of concentric glass pellets,one of the pellets being of such composition as to grip the ends of theelectrode sections and the other being especially adapted to bond to theinsulator, the two glass compositions uniting with each other onassembly.

Other objects and advantages of the invention will be pointed out duringthe course of the following description taken in connection with theaccompanying drawing in which:

Figure 1 is a longitudinal vertical section through the insulator withthe electrode assembled in it.

Figure 2 is a similar ilcation. v

Figure 3 is a fragmentary view similar to Figure 1 showing a modifiedconstruction as it appears prior to final assembly.

Figure 4 is a view corresponding to Figure 3 showing the parts as theyappear after final assembly.

Figures 5 and 6 are views similar to Figures 3 and ishowing a furthermodification.

Figure 7 is an enlarged section through the sealing pellet employed inFigure 3.

view showing a modi- Figure 8 is a corresponding section through thesealing pellet shown in-Figure 5.

In Figures 1 to 6, It indicates the spark plug insulator which may be ofany desired compocustomarily made of porcelain but may be madeofsintered oxides or mixtures oi oxides and silicates. Theinsu- I inassembling the insulators.

' cated at 30.

lator of Figures 1 and 2 is provided with a bore consisting of anenlarged upper portion I2 and areduced lower portion I4 connected byshoulder I6. In the enlarged portion I2 is provided the upper electrodesection I8 preferably having its lower end roughened as by means ofthreads or the like. The lower electrode section 22 is provided with anenlarged head 24 having sealing engagement at 26 with the lower end ofthe insulator. The upper end of the lower electrode section 22 ispreferably provided with a gasket 28 which may be of any suitable metalor other heat resistant material. The gasket is held in place by headingor riveting over the upper end of the electrode section 22 as shown. 32indicates conducting sealing material bonded to the electrode sectionsand to the insulator. In order to obtain a degree of mechanicalinterlocking with the insulator the latter may be provided with athreaded or otherwise roughened surface as indicated at 34. Theconducting material preferably consists of heat resistant glass, such asPyrex, mixed with powdered copper and fused in place as described in thecopending application of Schwartzwalder and Rulka, Serial No. 343,808,previously referred to.

In assembling the parts shown in Figure 1 the method described in theSchwartzwalder and Kirk Patent 2,106,578 and the previously mentionedapplication is preferably employed, that is, the sealing compositioneither in powdered form or pellet form is inserted in the bore betweenthe two electrode sections, the assembly is heated to soften the sealingmaterial and thereafter the electrode section I8 is pressed into place.i It is important to note that electrode section I8 is provided with ashoulder 36 which limits the extent of insertion of the electrodesection into the insulator bore. This insures uniformity Furthermore thesealing composition, when soft, yields to allow for any variations inthe length of the electrode parts thereby doing away with thenecessityfor accurate machining.

With the described construction the lower electrode section 22 is heldin place by the grip on the insulator resulting from the riveting indi-Consequently there is tight sealing engagement between the electrode andthe insulator at 26 and at the same time the washer 28 prevents thesealing composition 32 from entering the lower portion of the insulatorbore. The upper electrode section 20 is securely held in place by thesealing composition.

In this and the succeeding designs, it is desirable to make the lowerelectrode section of metal or alloy that is resistant to heat andcorrosion. The upper electrode. section 20 may be made of good heatconducting material such as l'copper or the like.

The modification shown in Figure 2 is substantially the same as thatdescibed except that the washer 28' is merely a tight fit on'the lowerelectrode section 22. Another difference is that a mechanical interlockis provided between the upper end of the lower electrode section and thesealing composition. This may take the form of grooves or notchesasindicated at 38 into which the sealing composition is forced onassembly so that it grips the electrode section and prevents itsdisplacement.

Another difference in construction'consists in parts, a central part 2Iand a surrounding terminal portion 23 having a flange 25 correspondingto flange 36 of the form shown in Figure 1. The part 2| is headed orriveted over'as shown at 21 to retain terminal 23.

In the modification shown in Figures 3 and 4 the electrode is indicatedas made of three parts. The lower part I22 is made of heat resistantmetal or alloy and is provided with shoulder I24 to limit its insertioninto the lower end of the insulator bore, and with an undercut portionI26 for interlocking engagement with the sealing composition I28. Thesealing composition is preferably prepared in the form of a centralcylinder I30 with a surrounding cylindrical shell I32. The portion I30may be made of a mixture of glass and metal characterized by ability tobond well to the electrode metal. For'this purpose the followingcomposition may be used:

Percent Lead borosilicate glass 50 Copper 50 The shell I32 is preferablyof a similar glassmetal composition characterized by ability to bondWell to the insulator as well as to the sealing composition I30. Thefollowing is a satisfactory composition for this purpose:

. Percent Borosilicate glass 55-30 Copper 45-70 134 indicates anintermediate electrode section having a lower reduced and undercutportion I36 similar to the part I26 of the lower section I22, exceptthat thereduced portion has a gradually tapered connection with the bodyof the electrode section.

Electrode section I34 may have its upper end slotted as shown and seatedin an enlarged portion I40 of the insulator bore. Electrode section I34may be suitably bonded to upper electrode section I 42 by sealingcomposition I44 in the manner previously described. The sealing isaccomplished in the manner previously described, that is, the assembledparts are heated to soften the sealing material and thereafter theelectrode sections are forced into the bore until the lower electrodesection assumes its position shown in Figure 4. In this embodiment theglass interlockswith the ends of the electrode sections to hold theparts assembled.

The form of the invention shown in Figures 5 and 6 is substantially thesame as that shown in Figures 3 and 4 except that the sealingcomposition is made in the form of concentric pellets I50 and I52adapted to encircle the adjacent reduced and undercut portions I26 andI28 of the electrode sections. After final assembly the parts assume theposition shown in Figure 6.

I claim:

1. A spark plug comprising an insulator having a bore therein, anelectrode in said bore making the upper electrode section 20' in twocomprising a lower section having an end serving as a sparkingelectrode, an upper section having a terminal for connection with asuitable lead and an intermediate electrically conducting sealinterposed between said electrode sections, and means on said uppersection for limiting the extent of insertion of the upper section intothe bore so as to insure a gap filled with said conducting seal betweensaid sections.

2. A spark plug comprising an insulator having a bore therein, anelectrode in said bore comprising a lower section having an end servingas a sparking electrode, an upper section having a terminal forconnection with a suitable lead and an intermediate electricallyconducting glass seal interposed between said electrode sections,

and an annular flange on said upper section for limiting the extent ofinsertion of the upper section into the bore so as to keep saidelectrode sections out of direct contact.

3. A spark plug comprising an insulator having a bore therein, anelectrode in said bore comprising a lower section having an end servingas a sparking electrode, means on said section cooperating with saidbore to prevent said section from passing out through the sparking endof said bore, an upper section having an end serving as a terminal forconnection with a suitable lead, an intermediate conducting seal, saidupper section being provided with stop means cooperating with the upperend of the insulator to limit the extent of insertion of the uppersection into the bore so as to keep said sections out of direct contact.

4...A spark plug comprising an insulator having a bore therein and'anelectrode in said bore comprising a lower section having an enlarged endserving as a sparking electrode and engaging the lower end of theinsulator to seal the bore against the entrance of hot combustiongases,' means adjacent the upper 'end of said section cooperating withsaid bore to prevent said section from passing out through the lower'end of the bore, an upper section having a terminal for connection witha suitable lead, and an intermediate-conducting seal bonded to theelectrode sections and the insulator.

5. A spark plug comprising an insulator having a bore therein, the lowerportion of the bore being of reduced diameter, an electrode in said borecomprising a lower section having an enlarged en d serving as a sparkingelectrode and having gas-tight sealing engagement with' the lower end ofthe insulator, means on said section above said reduced portion of thebore'engaging the shoulder between said bore portions to prevent saidsection from passing out through the lower end of the bore, an upperelectrode section having a terminal for connection-with a suitable leadand an intermediate conducting seal bonded to the electrode sections andto the insulator. 1

6.'A spark plug comprising an insulator having a bore therein and anelectrode in said bore comprising a lower section having an enlarged endserving as a sparking electrode and engaging the lower end 'of' theinsulator to seal the bore against the entrance of hot combustion gases,means adjacent the upperend of said section cooperating with said boreto prevent said section from'passing out through the lower end of thebore, an upper section having a terminal for connection with a suitablelead, and an intermediate conducting seal bonded to the electrodesections and the insulator, said upper'section being provided with stopmeans cooperating with the upper end of the insulator to limit theextent of insertion of the upper electrode section into the bore so asto keep said electrode sections out of direct contact.

7. A spark plug comprising an insulator having a bore therein, anelectrode in said bore com prising a lower section having a sparkingelectrode portion and an upper section having a terminal portion, ingseal separating said portions and bonded to the electrode sections andthe insulatonone of said sections being formed to mechanically interlockwith said seal to prevent its withdrawal from the bore.

8. A spark plug comprising an insulator having a bore therein, anelectrode in said bore comprising a lower section having a portionserving as a sparking electrode, an upper section having a terminalportion, and an intermediate conducting seal separating said portionsand bonded to the electrode sections and the insulator, said sealcomprising a central portion especially adapted to bond to the electrodesections and the surrounding portion especially adapted to bond to saidinsulator, said portions being integrally joinedtmeach other.

9. The method of assembling electrodes in spark plug insulators whichconsists in providing an insulator with a bore therein, inserting anelectrode in the lower end of the bore, thereafter inserting in saidbore fusible electrically conducting sealing material composed of acentral portion especially adapted to bond to the electrode material anda surrounding portion especially adapted to bond to the insulator andthen inserting in said bore the,upper electrode section; heating theparts so assembled to soften said fusible sealing material andthereafter pressing one of said electrodes into the bore to cause thesealing material to flow about the ends of said electrodes and thesurrounding portions of the bore and thereafter permitting said assemblyto cool so that the sealing material hardens and forms a gas-tight bondwith the electrode sections and the insulator.

TAJNE G. McDOUGAL.

and an intermediate conduct

